A conventional flat cable connector assembly is used for connecting two electrical devices separated from each other a relative long distance. The assembly has a flat flexible cable having a plurality of conductors therein for transmitting signal. The conductors are connected with respective terminals of connectors of the assembly. As transmitting speed is increased between the electrical devices, a flat coaxial cable is used for transmitting high speed signal. The flat coaxial cable comprises a plurality of parallel and equally spaced signal transmission lines, each line being constructed by a micro coaxial cable consisting of a central conductor, a layer of insulation surrounding the conductor, a metal braid surrounding the insulation and a jacket surrounding the metal braid as disclosed in U.S. Pat. No. 6,123,582 and the copending application Ser. No. 09/350,942 filed Jul. 9, 1999. Although such design can avoid cross talk between neighboring two lines, it still has a relatively large electrical skew, failing to meet the electrical performance requirements. Hence, an improved coaxial flat cable connector assembly is required to overcome the disadvantages of the presently used flat cable connector assemblies.